The broad goal of this research is to apply advanced imaging techniques to develop, in a patient-specific manner, a quantitative understanding of how the joints function, and of how they are affected by soft-tissue injuries and by their surgical treatment. The central hypothesis is that this understanding will lead to reliable, early and improved diagnostic and therapeutic procedures for joint ailments involving soft-tissue injuries. The focus of this proposal is on the ankle joint and its ligament injuries. The Specific Aims are: (1) to investigate ankle flexibility characteristics associated with specific ligament injuries; (2) to determine relative internal bone movements at the ankle and subtalar joints associated with ligament injuries; (3) to develop stress radiography and stress slice MRI that are optimum to show bone displacements associated with specific ligament injuries; and (4) to objectively assess the stabilization achieved by surgical reconstruction techniques for treating ligament damage. To fulfill Aim 1, a special mechanical device will be built and flexibility data will be gathered from normal injured, and post-surgical joints. To fulfill Aim 2, methods of MRI imaging under stress, image segmentation, 3-D reconstruction, and 3-D analysis will be developed. The resulting injury-specific internal displacement data will be utilized to devise simple, cost-effective methods, such as stress radiography and stress slice MRI, that best show the effect of injury (Aim 3). Such data will be used to objectively assess surgical reconstruction techniques based on pre- and post-operative scans and measurements (Aim 4). The expected outcomes of this research are twofold: (1) simple, cost-effective and high specificity methods of diagnosing ankle ligament injuries; and (2) new knowledge about the exact displacements occurring at the ankle and subtalar joints as a result of ligament injuries or their surgical repair.